Process and pollution-treatment particulate material for effecting removal of sulfur oxide gases from stack gases

ABSTRACT

A solid pollution-treatment product consisting of a core material of lime, quicklime or hydrated lime. The core is surrounded by a cracked shell formed of either calcium sulfate or calcium carbonate, such materials being referred to in this and prior applications of inventor by the coined terms &#34;Linfans&#34; and &#34;Linveins&#34;, respectively. 
     The described particulate material is particularly reactive to sulfur oxide bearing gases. Reactivity of such core material is even further enhanced by increasing its porosity through hydration and used in either the hydrated form or a selectively, partially or wholly dehydrated form before exposure to the sulfur oxide pollutants intended to be removed from flue gas or the like.

This is a division of application Ser. No. 286,016, filed July 22, 1981,now U.S. Pat. No. 4,387,078 issued June 7, 1983.

RELATED INVENTIONS

In previously filed related applications and issued patents, I havedisclosed, for example, in U.S. Pat. No. 3,781,408 "Air PollutionControl" an improved material for desulfurization described as"Linfans". Linfans consist of a core of porous unspent lime which issurrounded by a cracked shell of calcium sulfate. This material isadvantageously reused and recycled for desulfurization.

Similarly, I have disclosed, a new material similar to Linfans butdesignated as "Linveins" and which consists again of a core of porousunspent lime but instead of surrounded by calcium sulfate, is surroundedby a cracked shell of calcium carbonate which again is useable fordesulfurization and is fully disclosed in my now issued U.S. Pat. No.3,855,125. In my co-pending application Ser. No. 025,910 filed Apr. 2,1979, I reveal a further new material which is made up of a core ofporous hydrated lime having a cracked outer coating of calcium sulfateand useable for desulfurization, this being known as "Linfans H".

In those instances where the hydrated core is subsequently dehydrated,and prior to further reaction, I now designate the dehydrated core whichhas been previously hydrated, by the coined term "Linfans Q."

It is the use of these previously disclosed designated materials in anew and different manner of the present application, which constitutesthe subject matter of this filing.

BRIEF SUMMARY OF THE INVENTION

I use as a starting material, a porous core of calcium oxide, which issurrounded by a cracked shell of either calcium carbonate or calciumsulfate. This is derived by passing lime, quicklime or hydrated limethrough a reactor containing flue gases rich in sulfur trioxide. Thereaction product is then quenched rapidly in a dry state to effect thedescribed cracked outer shell of calcium sulfate.

The so described material is then hydrated either by water, moist air orsteam and is then recycled to the reactor at a selected location whichwill cause the material to futher react with the sulfur trioxide. The sodescribed reaction product is recycled to the reactor to a preferredlocation in the reactor so that the thermal shock will produce aparticle size of reactant of a desired size. Thus, greater thermal shockis made effective for fracturing the sulfur trioxide-calcium oxidereaction product producing it in even finer form. Conversely lessthermal shock will tend to preserve the original size of the sulfurtrioxide-removing product. Also the pollution-removing product can bepreheated gradually, to minimize the effects of thermal shock change inparticle size. Likewise, instead of returning the pollution-removingproduct in hydrated form, the product can be either partially or whollydehydrated prior to recycling to the reactor.

An important aspect of the present invention is that the sulfur trioxidegas removal is performed continuously by supplying continuous flow offlue gases rich in sulfur trioxide to the reactor, continuously cyclinglime or limestone supply through the reactor, and recycling the reactionproducts to the reactor.

Also, the gaseous outlet from the reactor may be quenched and hydratedby spraying water, passing the so resulting product through a solidseparation system then venting the sulfur trioxide free gas as aneffluent and thereafter recycling the quenched product in the form of"Linfans" or "Linveins" for additional passage through the reactor.

As a result of the foregoing, the following qualities of the reactionproduct which is intended for sulfur trioxide removal are obtained--thereactivity of the core of lime material is greatly enhanced, theporosity of the lime is improved, the surface area to unit volume ratioof the lime is increased, overall effectiveness of desulfurization isenhanced, and the lime is more efficiently utilized for desulfurizationthus reducing the amount of lime with its attendant reduction of cost oftransportation and volume of waste product. Moreover, the resultingreaction product of calcium oxide and sulfur trioxide, and the sulfurtrioxide-removing active ingredient better serves as a plasteringmaterial.

"Linfans, Linveins" can also be advantageously used for SO₂ removal justas SO₃.

BACKGROUND OF THE INVENTION

Briefly, in my air pollution control process, hot product particlesreleased from a lime reactor and used for desulfurization are quenchedrapidly. Quenching induces tension at the surface and compression at thecenter of the particle and the tension causes cracks in the CaSO₄coating of the particle. Furthermore, compression may causedisintegration of the lime core. The particles with lime in the core arecoated with cracked CaSO₄ coating are called Linfans, and are suitablefor desulfurization of stack gas. When Linfans are re-used or recycledfor desulfurization, the lime in the core of the particles is easilyreachable by the gas containing SO_(x) through the cracks of CaSO₄coating. When the SO_(x) in the gas is in contact with the lime in thecore of the particle, the following reaction takes place:

    SO.sub.3 +CaO→CaSO.sub.4

The reaction is very rapid and complete. Evidently, the sulfur trioxideis easily removed from the gas diffused into the particle, resulting inhigh SO₃ concentration gradient in the gas in the particle and effectinga high diffusion rate of SO₃ through cracks in CaSO₄ coating. Thus, theSO_(x) of the gas in the lime reactor is continuously removed.

It can be seen that the whole desulfurization process involves quenchingthe hot particles from lime reactor, inducing CaSO₄ coating cracks,increasing reactivity of the unspent lime in the core of the particle,and recycling the reactivated lime bearing particles for furtherdesulfurization. The use of Linfans (lime particles coated with crackedCaSO₄ coating) for desulfurization has not been achieved or attemptedbefore, and is new.

The production of "Linfans H" material from my desulfurization processcan be described as follows: The hot particles from lime reactor used indesulfurization are quenched rapidly by water, steam, pressured steam,or moist air. Quenching with water having high heat capacity and highheat of vaporation will result in the creation of cracks of CaSO₄coating. As a result, the lime in the core of the particle is reachableby water, steam of moistened air through the cracks. Thus, during thequenching process, hydration of lime also takes place in the core of theparticle and the reaction can be expressed as follows:

    CaO+H.sub.2 O→Ca(OH).sub.2, ΔH=-19.4 KCal/Mole

The intense chemical heat generated from the hydration process istemporarily prevented from dissipation to the surrounding environment bythe heat insulated CaSO₄ coating, thus resulting in a sudden rise oftemperature of the interior of the particle, which in turn, causes theparticle to expand. The core of the hydrated lime becomes a very porousmaterial, having greater surface area to unit weight ratio and greaterreactivity. The particles having a porous hydrated lime core and crackedCaSO₄ coating can be advantageously used for desulfurization of stackgas; for the hydrated core of of the particle is reachable by the gascontaining SO_(x) through the cracks of CaSO₄ coating. In a hot-drydesulfurization process, when the particles are added to a hot reactorenvironment, dehydration of hydrated lime in the core of the particletakes place according to the following formula:

    Ca(OH).sub.2 →CaO+H.sub.2 O, ΔH=19.4 KCal/Mole

It can be seen that after the water is driven from the hydrated limelattice in the dehydration process, the resulting quicklime in the coreof the particle is even more porous than that of the original hydratedlime, and is also more reactive with SO_(x) in the desulfurizationprocess. The rate of dehydration is expected to be rapid, for the rateof dehydration is dependent on the sizes of hydrated lime grains in thecore of the particle and on the temperature in the lime reactorenironment. The smaller the size of hydrated lime grain and the higherthe temperature of the lime reactor environment, the faster thedehydration rate will be.

From the described process for producing Linfans H material and fordesulfurization it can be seen that it involves quenching, hydration,and dehydration in sequence, and one of the new materials has a coinedname "Linfans Q." Linfans Q has very porous quicklime core coated withcracked CaSO₄ coating. This material had never been used previously fordesulfurization of stack gas before, and is very effective in SO_(x)including SO₂, SO₃ removal. The mechanism of desulfurization by "LinfansH" and its modified form "Linfans Q" are the same as that by Linfansexplained previously.

"Linveins" material, i.e. calcium oxide coated with fractured CaCO₃coating can also be used for desulfurization. When "Linveins" materialis added to the gas containing SO₃, the CaCO₃ reacts with SO₃ to becomeCaSO₄ according to the following equation:

    SO.sub.3 +CaCO.sub.3 →CaSO.sub.4 +CO.sub.2

This reaction takes place on the surface of the CaCO₃ coating. SO₃ inthe gas can seep through the cracks of "Linveins" to react with CaO inthe core to form CaSO₄, and the mechanism of SO_(x) removal is similarto "Linfans".

Desulfurization by "Linveins" can also be achieved after the calciumoxide core is hydrated to become porous hydrated lime, and thedesulfurization process involves quenching, hydration, dehydration, limereaction with SO_(x). The mechanism is the same as that in thedesulfurization with hydrated lime coated with thermal shock fracturedCaSO₄ coating explained previously.

When "Linfans" or "Linveins" particles, having either quicklime orhydrated lime core coated with CaSO₄ or CaCO₃ coating, are applied to ahot reactor environment for desulfurization, the sudden heat shock mayinduce fragmentation of the lime core and result in more porous lime.However, heating also causes the particle to expand, and if the CaSO₄ orCaCO₃ coating strength is weak, the particle will disintegrate into manytiny particles. This may present material transportation and solidmaterial separation from the gas problems which may be undesirable inmany cases. In order to prevent this, heating the particles gradually orby stages to the reactor temperature inside or outside the reactorbefore desulfurization is the solution.

Linfans, Linfans H, Linfans Q, and Linvein can be efficiently used forSO₂ removal in other dry scrubbing processes. When they are added to theflue gas containing SO₂, SO₂ diffuses through the cracks of either CaSO₄or CaCo₃ shell to react with lime core according to the followingformula:

    SO.sub.2 +CaO→αCaSO.sub.4 +βCaSO.sub.3 +γCaS

The extent of CaSO₄, CaSO₃, and CaS in the reaction product depends onreaction temperature. However, in a high temperature environment, mostof the resulting product is CaSO₄. Since the chemical heat generatedfrom this reaction is high, and can not be easily dissipated within theshell, therefore, the resulting product from the chemical reaction isexpected to be CaSO₄. The reaction mechanism of SO₂ removal in theparticle having a cracked shell is the same as that of SO₃ removal whichhas been explained previously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the complete process forproduction of "Linfans" material, consisting of cracked CaSO₄ coatingwith a lime core useable for recycling the material for desulfurizationin the manner indicated;

FIG. 1A is a cross sectional view of Linfans;

FIG. 2 is a schematic view showing the process for producing "LinfansQ", a coating of cracked CaSO₄ over porous lime, and for recycling thematerial for desulfurization;

FIGS. 2A and 2B are cross sectional views of Linfans H and Linfans Q;and

FIG. 3 is a schematic view showing the process for producing "LinfansH", a coating of cracked CaSO₄ and a core of hydrated lime, and forrecycling the material for desulfurization.

DETAILED DESCRIPTION OF EMBODIMENT OF FIG. 1

In FIG. 1 are shown a source of SO_(x) 10 which can be a furnace, oreroaster, smelter, etc. The gas from the source of SO_(x) 10 containsSO₂, SO₃, and suspended solid particles. The gas is passed through asolids separation system 12 which can consist of electrostaticprecipitators, filters, or others. The solid separation system shouldhave nearly 100% solid removal efficiency, particularly with regard tothose particles which may poison catalysts in the catalytic oxidationconvertor 14. Separated fly ash particles are collected, quenched, ifdesired, and sent to a storage bin 20 for future use.

When vanadium catalyst is used, the flue gas is cleansed of suspendedparticles, and is then temperature regulated or adjusted to 650° F. to950° F., preferably to between 850° and 880° F. The catalytic conversionfrom SO₂ to SO₃ is expressed by the following reaction:

    SO.sub.2 (g)+1/2O.sub.2 (g)→SO.sub.3 (g)

The flue gas rich in SO₃ from catalytic convertor 14 flowscountercurrent with lime, and the following reactions take place in thereactor 16:

    SO.sub.3 (g)+CaO(s)→CaSO.sub.4 (s)ΔH=-96K cal/mole

or

    SO.sub.3 (g)+H.sub.2 O(g)→H.sub.2 SO.sub.4 (g)

    H.sub.2 SO.sub.4 (g)+CaO(s)→CaSO.sub.4 +H.sub.2 O(g)

Lime is fed into the reactor 16 from lime supply 18. Since the chemicalheat generated from the chemical reactions in the reactor 16 is veryhigh (96K cal/mole) the heat can be advantageously employed forcalcination in some cases. Therefore, limestone can be used as asubstitute for lime if SO₃ concentration in the incoming gas to limereactor 16 is high.

The solid particles from reactor 16 are quenched in a dry state inquenching unit 22, and the resulting product, "Linfans", FIG. 1A, iscollected in "Linfans" storage 34.

The exit gas from lime reactor is first passed through a heat exchanger28 such as economizer, and then a solids separation system 30. Theeffluent flue gas is free from solid particles and SO_(x). The solidparticles from solids separation system 30 is quenched in a dry state ina quenching unit 32, and the resulting particles from quenching unit 32is "Linfans" which is also collected in "Linfans" storage 34.

"Linfans" is recycled to lime reactor 16 at different points as desired.If a multi-stage fluidized reactor is employed, in order to preventthermal shock, "Linfans" can be fed to the upper stage or cold zone ofthe reactor. As "Linfans" flows downward from upper stage or lowerstage, it extracts heat from the counter-current gas and is heatedgradually or by stages. On the other hand, if thermal shock is desiredfor the reason of causing "Linfans" particles to disintegrate or ofmaking the lime core of the particles more porous, "Linfans" can beapplied to the reactor at lower stage or hot zone.

FIG. 1A is diagrammatic cross-sectional view of "Linfans" which hasunspent lime in core coated with cracked CaSO₄ coating.

DETAILED DESCRIPTION OF EMBODIMENT OF FIG. 2

In FIG. 2, the gas rich in SO₃ reacts with lime in reactor 16, the solidparticles from reactor 16 are quenched and hydrated by water, moist air,steam or pressured steam, in quenching and hydration unit 24, and theresulting product, "Linfans H" (FIG. 2A) is collected in "Linfans H"storage 35. The solid particles in the exit gas from lime reactor 16 arequenched and hydrated by fine spray in a duct or a chamber 36, and thenseparated from the gas in a solids separation system 38. The separatedsolids is "Linfans H", and is collected in "Linfans" storage 35."Linfans H" can be recycled from "Linfan" storage 35 to different pointsof lime reactor 16 as desired. Alternatively, it can be recycled to thereactor 16 after it is heated in a heating unit 40 to a desiredtemperature, and the dehydrated particles, "Linfans Q", from the heatingunit has a very porous lime core.

FIG. 2A shows diagrammatic cross-sectional view of "Linfans H" particlewhich has hydrated lime in core coated with cracked CaSO₄ coating. FIG.2B shows a diagrammatic cross-sectional view of Linfans Q which has veryporous lime core coated with cracked CaSO₄ coating.

DETAILED DESCRIPTION OF EMBODIMENT OF FIG. 3

In FIG. 3, the solid particles from lime reactor are first quenched inquenching unit 22 in a dry state and then hydrated by water, moist air,steam or pressured steam in hydration unit 26. Hydration can also beachieved by prolonged storage. The resulting product from hydration unitis Linfans H, having hydrated lime core coated with cracked CaSO₄coating.

The solid particles in the exit gas lime reactor are quenched andhydrated by fine spray of water in a duct or a chamber 36, and thenseparated from the gas in a solids separation system 38. The applicationof fine spray of water to the gas cools at the same time also the gas,thus, reduces the volumetric flow rate of the gas, and reduces thevolume of the gas to be handled by the solids separation system.Furthermore, the water picked up by the solid particles tends toincrease the conductivity of the particles, making them easy to beremoved in an electrostatis precipitator. The desired temperature ofeffluent flue gas is about 300° F.

The solid particles from solids separation system are Linfans H and arealso collected in Linfans H storage 34. Linfans H can be recycled fromLinfans H storage 34 to different points of lime reactor 16 fordesulfurization after it is heated gradually or by stage in a heatingunit 40 to a desired temperature. Linfans H can also be heated by stagesin the reactor 16, depending on equipment and process design.

DETAILED DESCRIPTION OF SPECIFIC WORKING EXAMPLE

Two materials, Linfans 1A (LF-1A) and Linfans Q 1A (LF-Q-1A) has beenused for desulfurization experiment. LF-1A was produced by reacting highcalcium lime with gas rich in SO₃ at 880° F. for 40 minutes in a tubereactor, and then quenched rapidly in air, while LF-Q-1A was produced inthe same manner except that it was quenched and hydrated by a fine sprayof water and then dehydrated in an oven at 880° F. for 30 minutes. LF-1Ais calcium oxide coated with fractured CaSO₄ coating, and LF-Q-1A isporous calcium oxide coated with fractured CaSO₄ coating.

The desulfurization experiments were conducted also in the tube reactorby reacting LF-1A and LF-Q-1A respectively with the gas rich in SO₃ at880° F. for 40 minutes. The chemical compositions of the Linfansmaterials were determined before the desulfurization and after thedesulfurization, and the results are shown in the following Table 1:

                  TABLE 1                                                         ______________________________________                                        Chemical Composition of Linfans 1A(LF-1A),                                    Linfans Q 1A(LF-Q-1A) Before and After the Desulfurization                           De-      Chemical Composition                                                                           CaO                                          Chemical sulfur-    Lime as              Con-                                 Used     ization    CaO      CaSO.sub.4                                                                          Others                                                                              version                              ______________________________________                                        Linfans 1A                                                                             Before Used                                                                              59.8%    36.8% 3.4%  20.3%                                (LF-1A)  for                                                                           After Used 25.9%    70.0% 3.2%  53%                                           for                                                                  Linfans Q 1A                                                                           Before Used                                                                              61.1%    35.2% 2.7%  19.2%                                (LF-Q-1A)                                                                              for                                                                           After Used 10.1%    88.2% 1.7%  72.0%                                         for                                                                  ______________________________________                                    

From the table, it can be seen that the Linfans materials are highlyreactive with SO₃, and the CaO conversion was increased from 20.3% to53% for LF-1A, and 19.2% to 72% for LF-Q-1A, resulting in much greaterutilization of CaO than ordinary lime for desulfurization. Evidently,the Linfans materials can be reused or recycled advantageously fordesulfurization.

INDUSTRIAL APPLICATION

The invention is usable for removing sulfur oxides as a pollutentingredient in stack gases by satisfactory treatment with an activatedcore of lime, having a cracked coating, calcium oxide, or calciumsulfate. The pollutent treating materials is used for rendering stackgases virtually pollution free.

CONCLUSION

I have ameliorated a serious problem of air pollution, SO_(x) removalfrom stack gas, in an economical and efficient manner, and satisified along-standing need for a commercially acceptable system for airpollution control. However, the process is not to be construed aslimited to the particular forms described herein, since these areillustrative rather than restrictive. For example, chemicals other thanCaO may be used to stabilize at least one of SO₂ and SO₃ gases to formstable, nongaseous chemical product which can be easily disposed.Magnesia, MgO, closely resembles CaO, is almost invariably present incommercial lime. It reacts with SO₂, SO₃ to form MgSO₄ just like CaO. Anelectron beam instead of chemical catalyst can be used for conversion ofSO₂ to SO₃.

Although the present invention has been illustrated and described inconnection with a few selected example embodiments, it will beunderstood that they are illustrative of the invention and are by nomeans restrictive thereof. It is reasonable to expect that those skilledin this art can make numerous revisions and adaptations of the inventionand it is intended that such revisions and adaptations will be includedwithin the scope of the following claims as equivalent of the invention.

What is claimed is:
 1. An active pollution-treatment ingredient in theform of a solid particulate material for effecting removal of sulfuroxides from flue gas, consisting of an outer cracked shell of calciumsulfate, and a core consisting of quicklime comprising a very porouscore material as a result of the core material, while surrounded by theouter cracked shell, having been hydrated and dehydrated through acontrolled hydration and dehydration process which maintains the corematerial within the core of the particulate material and the hydrationeffected by the controlled provision of moisture in the form of steam,moist air or sprayed water.
 2. The active pollution-treatmentparticulate material in accordance with claim 1, wherein the reactionproduct is characterized by an increased proportion of calcium sulfateto calcium oxide after exposure to the sulfur oxide gases.
 3. The activepollution-treatment particulate material in accordance with claim 1,wherein said ingredient is characterized by cracks of the outer crackedshell permitting diffusion of sulfur oxide gases through the cracks intothe core during reaction in a reactor.